Device for conference calls in subscribers&#39; devices for loud and faintly audible traffic



o. TSCHUMI Sept. 14, 1948.

FOR LOUD AND FAINTLY AUDIBLE TRAFFIC Filed May 12, 1944 inventor a m LB 2... N 1 in 6 My My K 4 u u w N u mW 3 5%---- a M Pate'nted Sept. 14, 194$ "UNITED STATES PATENT (OFFICE I I 4 2,449,344 DEVICE FOR CONFERENCE CALLS IN SUB SCRIBERS DEVICES FOR LOUD AND 'FAINTLYAUDIBLE TRAFFIC Otto Tschumi, Soleure, Switzerland, assignor to Autophon Aktiengesellschaft, Soleure, 'Switzerland, ajoint-stock company of Switzerland.

Application'May 12, 1944, Serial NOL'535,298 1 I In Switzerland December 10, 1942 2 Claims.

This invention relates to devices for conference calls in subscribers devices for loud and faintly audible signals.

If one of several subscribers should have the possibility of calling together any number of other subscribers for a loud or faintly audible telephonic conference, a considerable number of additional switch devices was hitherto necessary.

The device accordin to the invention allows switch devices already existing in the installation to be used in such a way that the above-mentionedconnections become "possible, thus allowing conference calls to be carried out economically. The device according to thewinvention is characterised in that the means, serving in normal communication from subscriber to subscribertfor changing-over loud to faintly audible signals, are used for switching-in the microphone of a subscriber wishing to speak at the conference.

The accompanying drawing illustrates, by way of example, one embodiment of the invention,

Figure 1 shows the diagram of a subscribers device, and

Fig. 2 illustrates in a diagrammatic way that part of the main station which is necessary for the comprehension of the invention.

The electro-acoustic transformer EW shown in Fig. 1, accordin to the manner in which it is connected to the amplifier V, works as a loudspeaker or as a microphone. It is connected with the terminals a, b over the repeater Ue, the middle of the repeater-winding on the side of the line being in electric connection with the terminal a over the receiver T and the switch TK1, so that by this current path one coil-half is bridgedover. The middle of an impedance coil Dr placed between the terminals a and b is connected with a rectifier arrangement over the contacts ES and 62 which, in their turn, are bridged-over by the condenser CI. The rectifier arrangement is earthed over the impulse contact 2' of the calling dial NS and comprises an element (relay E) independent cf the land and direction of current and elements (relay U, optical signal SZ and resistance W3) dependent on the kind and direction of current. Relay U can be disconnected from the rectifier arrangement by the switch TK2 and the resistance We by the switch TKs. In Fig. 2 Tr means a transmission transformer. The middle of the winding of the transformer lying on the side of the main station can be connected alternately to a negative direct current potential or an alternating current source over the contacts I01 and m. The transmission conductors lead to the branch exchange final selector. Line it goes to :the multiple contacts 21 andcz which, as the multiplecontact as, are controlled :by the relay Z inserted into the n-line of the c-core. Relay Z is, similar to relayTs, connected to .a negative direct currentrpotential, and its circuit is closedwhen it is connected by thebranch exchange final selector LWc to the positive side of a battery over relay K, relay P and thecontact p.

Figure 3 shows the delay action relay N connected inseries with the contact 702. w

If the subscriber of the subscribers, device 11- lustrated in Fig.1 wishes to call. together a conference he establishes ".2. connection with theaterminals a, b of the transmission transformer'Ir in Fig. 2 by dialling the dial NS. Thefinalselector LW with its arms LWa-c is now adjusted corresponding to theselecting impulses, for in-- stance, adjusted on the line 12. Thereby the above-mentioned circuit is closed for the relay Z, which results in the fact that by the multiple contacts 21-3, the subscribers desired are selected and switched-in. Thereby, also the relays T1 and T5 of the subscribers in question are operated so that they are locked against any further call.

Owing to the fact that the relay Z is of smaller resistance than relay Ts, into the place of which it steps owing to the selected number of impulses, relay K comes into action and by the contact In causes, that in place of the normal voltage a short alternatin voltage is given upon the subscribers devices. The other contact k2 of the relay K operates the delay action relay N effecting the disconnection of the alternatin current source and the substitution of the latter by a negative direct current potential, so that only during the short period within which the attraction of the relay N is delayed with regard to relay K owing to the condenser connected in parallel, the subscribers devices are supplied with alternating current.

This short alternating current impulse reaches over condenser CI the relay E of the rectifier arrangement which results in a connecting-in of the amplifier by the switches c1 and e: and in the opening of a direct current path over the rectifier arrangement. Thereby, relay U is operated and all the stations in question are changed over to hearing condition.

If one of the subscribers called for the conference wishes to change over from hearing to speaking, he takes off the receiver T, thereby operating the switches TKl-Il. The relay U is disconnected from the circuit by switch TK2, and the switches in and ma change over the electroacoustic transformer EW to speaking conditions. TKl connects the receiver to the line, so that the speaking person can examine whether another person enters into conversation in his place. After havingspoken the subscriber in question replaces the receiver T, switch 'I'Ki is opened, while switch TKz again connects in the relay into the direct current circuit, whereby EW is again changed over to speaking conditions.

.As may be seen from the above, all the subscribers participating in the conference can by individual means establish conditions allowing them to speak. This coordination of the stations is only interrupted by the factthat the station having called together the conference has the additional possibility of establishing the speaking conditions by operating the calling dial Should some of the subscribers not desire to hear the conference through the loud-speaker, but only faintly audible, they may constantly hold the receiver to the ear, while the transformer EW remains continuously disconnected from the line by keeping open the contact AS. These' means, allowing any of the conference participators to insert himself as a speaker into the conversation, serve in normal traffic the purpose of changing-over a loud conversation into a faintly audible one and vice-versa in that, by removing the receiver, EW is changed-over to speaking conditions and receiver T connected to the line.

In this way, it is possible to combine both operations with the aid of the same switch devices which, besides a simple connection, results in smaller costs. a

What I claim is: l

1. In a telephone system for loud and faintly audible communication, subscribers stations each including an electro-acoustic transformer serving as both a microphone and a loud-speaker, a line circuit, connections between said circuit and said electro-acoustic transformer, circuit control means operable to change said connections to render the electro-acoustic transformer operative as either a microphone or loud-speaker, means responsive to an incoming signal to operate the circuit control means and render the electroacoustic transformer operative as a loud-speaker, a normally inoperative receiver for producing faintly audible signals, and switch means for operably connecting said receiver in said circuit and simultaneously rendering said signal responsive means inoperative whereupon said electroacoustic transformer is rendered operative as a microphone by said circuit control means.

2. A telephone system as claimed in claim 1 wherein each subscribers station is provided with a calling dial for selecting other of said stations to be called.

OTTO TSCHUMI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,162,547 Campbell June 13, 1939 2,192,540 Creti Mar. 5, 1940 2,214,992 Chevassus Sept. 17, 1940 2,224,698 Roseby Dec. 10, 1940 2,247,507 Lanham et al. July 1, 1941 2,346,504 Place Apr. 11,1944 

